This invention relates to a method of generating a signal for transmission. More particularly it relates to a method of generating a signal for multiple access transmission. It also relates to a method of receiving such a signal.
The invention relates to a block CDMA scheme that is general by nature, but encompasses several special cases, two of which are reduced-complexity multiple access techniques that are related to OFDMA and SC-FDMA.
Code division multiple access (CDMA) is a popular multiple access technique that is used to support multiple users simultaneously in a network. Many variants of CDMA exist, including direct sequence (DS) CDMA, multi-carrier (MC) CDMA, cyclic prefixed (CP) CDMA, and chip interleaved block spread (CIBS) CDMA. In addition to these variations, many receiver architectures are often available for implementation in CDMA systems, such as the well-known RAKE receiver, interference cancellation receivers, and receivers that rely on channel equalisation.
Some CDMA schemes are interference limited; that is to say, as the number of users in the network increases, residual interference caused by each user eventually also increases and eventually cripples the network, thus rendering simultaneous multiple access nearly impossible. This residual interference generally results from the loss of orthogonality amongst users, which primarily occurs when the channel is temporally dispersive.
Several recent developments in block CDMA systems, including so-called ‘generalised MC-CDMA’ (GMC-CDMA), CIBS-CDMA, single-carrier frequency division multiple access (SC-FDMA) (also known as DFT-spread OFDM), and a throughput-efficient block CDMA system, have led to multi-user interference (MUI) free transmission techniques.
US 2004120274, incorporated herein by reference, discloses CDMA transceiver techniques for wireless communications.
US 2002126740, also incorporated herein by reference, proposes chip-interleaved, block-spread multi-user communication.
An example of a so-called ‘generalised MC-CDMA’ system is described in “Wireless multicarrier communications”, Zhendao Wang, Giannakis, G. B., Signal Processing Magazine, Vol. 17, No. 3, pages 29-48, May 2000, incorporated herein by reference.
Shengli Zhou, Giannakis, G. B., Le Martret, C. describe a system using CIBS-CDMA in: “Chip-interleaved block-spread code division multiple access”, IEEE Transactions on Communications, Vol. 50, No. 2, pages 235-248, February 2002, incorporated herein by reference.
Single-carrier frequency division multiple access using DFT-spread OFDM is described in “Performance comparison of distributed FDMA and localised FDMA with frequency hopping for EUTRA uplink,” NEC Group and NTT DoCoMo, TSG RAN WG1 Meeting 42 R1-050791, August 2005, incorporated herein by reference, and “A low complexity transmitter structure for OFDM-FDMA uplink systems”, D. Galda and H. Rohling, in Proceedings of the IEEE Vehicular Technology Conference (VTC), Vol. 4, pages 1737-1741, May 2002, also incorporated herein by reference.
A throughput-efficient block CDMA system has been proposed by S. Tomasin and F. Tosato: “Throughput Efficient Block-Spreading CDMA: Sequence Design and Performance Comparison” in: Proceedings of the IEEE Global Telecommunications Conference (Globecom), November-December 2005, incorporated herein by reference.
In these systems, any number of users—up to a given maximum number—can theoretically transmit simultaneously without causing any degradation in system performance. However, beyond this maximum number of allowable users, the system becomes interference limited in a similar manner to other CDMA systems.